There are existing optical elements that are capable of changing the refractive power thereof by changing the curvature of the interface between two optically transmissive materials (e.g., liquids).
FIG. 11A illustrates a variable refractive power element 100 including two liquids that do not mix with each other. Electrodes 101, which are covered with insulators, are disposed so as to be in contact with liquid 103 and liquid 104. In addition, electrodes 102 are disposed so as to be in contact with the liquid 103. When a voltage is applied between the electrodes 101 and the electrodes 102, electric charges are generated on the surfaces of the electrodes 101, so that the balance of the tension generated between the electrodes 101 and the liquid 103, and the tension generated between the electrodes 101 and the liquid 104 is changed. Thus, the curvature of the interface between the two liquids 103 and 104 can be changed.
FIG. 11B illustrates a variable refractive power element 200 including an elastic film 203 between two liquids 201 and 202. The elastic film 203 is deformed by moving the two liquids 201 and 202 by using a driving unit 204, whereby the refractive power of the element 200 can be changed. For the variable refractive power element 200, liquids that mix with each other may be used as the two liquids 201 and 202.
Zoom lenses including the above-described variable refractive power element are known. Patent Literature (PTL) documents 1 and 2 each describe a zoom lens in which the movement amounts of lens units during zooming are reduced or eliminated by using a plurality of variable refractive power elements and thereby the total length of the zoom lens is reduced.
Patent Literature 3 describes a zoom lens that reduces variation in chromatic aberration due to zooming by changing the shape of the interface between different media having about the same refractive index and different Abbe numbers.
Citation List
Patent Literature
PTL 1 Japanese Patent Laid-Open No. 2006-98972
PTL 2 Japanese Patent Laid-Open No. 62-24210
PTL 3 Japanese Patent Laid-Open No. 62-78521
In an optical system including a variable refractive power element, the larger the magnification during zooming, the larger the change in refractive power during zooming, and larger the variation in chromatic aberration generated in the variable refractive power element.
The zoom lenses described in Patent Literatures 1 and 2 do not have measures against the variation of chromatic aberration due to zooming. Therefore, if the refractive power of the variable refractive power element does not change appropriately, the variation in chromatic aberration due to zooming becomes large.
The zoom lens described in Patent Literature 3 is capable of reducing the variation in chromatic aberration due to zooming. However, the refractive power does not change during zooming because the two media that form a deformable interface therebetween have the same refractive index. Accordingly, a high zoom ratio cannot be realized by using a change in the refractive power at the deformable interface.
In light of the foregoing state of the art, a zoom lens of the type described above is desired to offer a high zoom ratio and small variation in chromatic aberration due to zooming.